Mammography examinations of women aged 40-49 reduce breast cancer mortality by 29%, a statistically significant reduction. This is shown in the Umeå University-directed national SCRY Study in Sweden, which is the largest study of its kind ever performed anywhere in the world.
X-ray examination of all women's breasts with the aim of discovering breast cancer, so-called mammography screening, saves the lives of many women each year in that tumors are found early and can therefore be treated early. However, a lower age limit for mammography screening is necessary, as younger women run a lower risk of developing breast cancer, which means that more women would have to undergo mammography in order to save the corresponding number of lives. What's more, mammography works less well in younger women.
The SCRY Study (mammography SCReening of Young women) compares breast cancer mortality between a study group consisting of those counties/municipalities that have invited the age group and a control group consisting of areas that have only invited women aged 50 and older. Only deaths caused by breast cancer in the ages of 40-49 were counted. The average follow-up period was 16 years for both the study group and the control group.The study is the largest ever undertaken for the 40-49 age group in the world. Data from the cancer registry and the cause of death registry have been used. Further, individual data from screening centers throughout Sweden have been gathered, making it possible to study the effect both on women who were offered mammography and on women who actually participated.
The study covers the entire country. It comprises 803 breast cancer deaths over 7.3 million person years in the study group (which underwent mammography) and 1,238 breast cancer deaths over 8.8 million person years in the control group. The mean number of women aged 40-49 years in Sweden during the study period was 600,000. The study shows that breast cancer mortality was 26% lower for those who were invited to mammography screening compared with those who were not. Those who actually participated in mammography screening had a 29% lower breast cancer mortality rate than those who were not invited to screening. The findings are statistically significant.
A comparison between the group that underwent mammography and the control group that was undertaken for a period before screening started uncovered no statistically significant difference in breast cancer mortality. Breast cancer care in Sweden has moreover been further standardized since that time, not least as a result of care programs and national guidelines. This indicates that the difference in breast cancer mortality is a result of access to mammography screening among 40-49-year-olds.
There is a consensus today that mammography screening for the 50-69-year age group reduces breast cancer mortality. Calling in women aged 40-49 years for mammography screening, on the other hand, has been controversial and much debated since the 1980s, when mammography screening began. Few studies have been able to show any significant effect on mortality in the age group. At the same time, few studies have been designed to study the age group in particular. The Swedish National Board of Health and Welfare recommends screening for the entire age interval of 40-74 years, whereas EU guidelines do not include 40-49-year-olds in their recommendations. In the U.S., the U.S. Preventive Services Task Force (USPSTF) recently changed its recommendations not to include the 40-49 age group.
Originally the Swedish National Board of Health and Welfare recommended that women aged 40-69 years should be called in for screening. Soon after, these recommendations were changed to focus on women between the ages of 50 and 74. As a result, for a long period roughly half of Swedish counties and municipalities have called in 40-49-year-olds for screening, while about half have chosen to call in only women aged 50 and over.
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